United States Department of Transportation
i
Evaluation of Recycled Components in Stone Matrix Asphalt Mixes
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2023-12-01
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[PDF-2.78 MB]
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Edition:Final Report (July 2020-October 2023)
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Abstract:Currently, Missouri DOT (MoDOT) does not allow use of recycled materials in SMAs. MoDOT commissioned this study to investigate the effect of incorporation of recycled materials such as RAP and GTR in SMAs. In Phase 1, plant-produced mixtures were collected, and recreated under BMD methodology to determine acceptable upper-limit on RAP for initial implementation. In Phase 2, friction properties of mixtures were obtained by testing aggregates, lab and plant produced mixtures, and a field section containing GTR. Based on the results, the following conclusions were drawn: 1) The current use of conglomerate, unfractionated RAP stockpiles poses practical limitations in achieving passing BMD thresholds at higher levels of RAP, 2) Suitable frictional characteristics were achieved at lower levels of RAP but results indicated that the softer aggregates present in current RAP stockpiles tended to reduce skid resistance, and 3) Use of GTR appears to be promising option for incorporating recycled materials into Missouri pavements, based on lab BMD and skid resistance results in the lab and field. Based on the findings, the following recommendations were made :1) MoDOT should consider allowing RAP in SMA mixtures but, an upper limit of 15% asphalt binder replacement (ABR) from RAP is recommended at this time, 2) If greater than 15% ABR by RAP is considered, a value engineering proposal should be provided, accompanied with BMD tests, 3) The research supports the continued and increased usage of GTR as a possible approach towards achieving good mixture durability, skid resistance, and mixture sustainability.
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